In one aspect, this invention relates to insulators for clamping or holding an electrical conductor above the ground for aerial power distribution and transmission.
In another aspect, the invention relates to a method of stringing such a conductor on a plurality of insulators which are supported above the ground on a series of poles which are to form the distribution or transmission line.
The conductors may be either insulated cables or conductors of the bare wire type.
There has been a long-felt need for such an insulator which is economical to manufacture, at least the major portions of which may be made of moldable plastic material which has a low dielectric constant and is weather and track resistant, which is easy to manipulate to clamp or hold a conductor without damaging the conductor, which reduces radio and television interference, increases the leakage resistance path from conductor to ground, reduces the components of the insulator and is designed to accept a conductor stringing device which allows the conductor to be installed and tensioned on a plurality of insulators without the use of the customary stringing roller blocks or the usual temporary support of the conductor while the stringing device is removed and a permanent insulator is installed.
There has also been a long-felt need for a stringing method which is economical in use, which eliminates the use of stringing roller blocks and temporary support of the conductor while the stringing device is removed and the permanent insulator is installed and in which neither the insulator nor the stringing device is subjected to excessive wear when the conductor is pulled through the stringing device during the stringing steps.
U.S. Pat. No. 3,739,075 dated June 12, 1973 owned by Hendrix Wire and Cable Corporation, the assignee of the present application, discloses one unsuccessful attempt to meet said long-felt needs. In the insulator of that patent, the body of the insulator was provided with a cylindrical eye 15 having a circular passage 16 through which the conductor cable was pulled during the stringing step. Because the diameter of the passage 16 was much greater than the diameter of the conductor, it was necessary to use wire means 38, wire means 43 or elastic tie means 45 to hold the conductor in the passage 16. In addition, the cylindrical eye 15 was not made of a sufficiently wear resistant plastic to prevent excessive wear when the conductor was pulled through it during stringing.
Another attempt to fill the long-felt need is a metallic clamp made by Lapp Insulator Co., Inc. which is secured to the end of an insulator. It had a lower metallic member having a groove to receive the lower portion of the conductor and an upper metallic member which is placed above the upper portion of the conductor. These metallic members were clamped about the conductor by two metal bolts which passed into interiorly threaded passages. Lapp recommended use of a torque wrench to rotate the bolts to clamp the metallic members about the conductor with the correct amount of pressure to hold the conductor, the clamp was expensive to install and four different sizes were required to cover a range of conductors having diameters of from 1/4" to 11/2". In addition, when these metallic clamps were used with a covered conductor, a voltage difference existed between the conductor and the clamp and between the clamp and the metallic supporting base of the insulator, these voltage differences were not stable but varied with the weather conditions and the contamination and the arcing produced radio and television noise as as well as damage to the conductor covering material.
Reliable Electric Company's Synthetic Products Company Division, attempted to meet the long-felt need with a temporary stringing pin insulator which accommodates conductors up to 11/2" in diameter. This stringing pin insulator is shown in U.S. Pat. No. Des.235,190. As an accessory, a channel shaped replacable insert is available to limit wear of the temporary insulator but it is not cylindrical and cannot be rotated to distribute wear from job to job.
Other attempts to meet the long-felt need have been made by Lindsey Manufacturing Company of Pasadena, California. Each of them consisted of a six-piece metallic conductor clamp adapted for mounting on the end of a porcelain insulator. They each had the same deficiencies as the above described Lapp metallic clamp except that only one bolt was used to move one of the clamping members into gripping engagement with the conductors.
One of the Lindsey clamping assemblies is shown and described in U.S. Pat. No. 3,437,743. It comprises a metal bracket secured to an insulator. The main body of the clamp is pivotally secured in the bracket by a pintle and a cap screw. The main body has an upwardly facing conductor seat. A jaw is movable towards and away from the conductor seat by a second cap screw which acts against a lock washer. This clamping assembly is also shown in U.S. Pat. No. Des.209,667.
Another Lindsey clamping assembly is shown and described in U.S. Pat. No. 3,437,742 and Des.209,668. This assembly is similar to the assembly described above except that the jaw is movable vertically by the cap screw and its bolt can be tilted to a position in which the jaw does not cover the conductor seat.
The Lindsey conductor clamp shown in U.S. Pat. No. Des.213,049 is substantially the same as the clamp shown and described in U.S. Pat. No. 3,437,742 except that the bolt which actuates the jaw cannot be tilted.
To the best of our knowledge, the above described prior art is the closest prior art to the insulator and the stringing method of the present invention.